A typical musical instrument of the acoustic percussion family such as, for example, a xylophone or a marimba is provided with tuned bars in keyboard arrangement and graded in length to provided a chromatic scale of three or four octaves. When a performer strikes the tuned bars with rubber-tipped mallets, the bars vibrate at the respective natural frequencies which cause the bars to produce respective tones so as to make a fine melody.
However, in an electronic percussion system corresponding to the xylophone or the marimba, tones are produced by a tone generation unit incorporated in the system so that bars are only expected to detect forces exerted thereon upon performance. Then, a bar incorporated in the electronic percussion system serves as a force sensitive device and the structure thereof is illustrated in FIGS. 1 and 2.
Referring to FIGS. 1 and 2 of the drawings, there is shown the structure of the typical prior-art force sensitive device serving as a bar incorporated in an electronic percussion system. The prior-art force sensitive device comprises a lower conductive sheet 1, an upper conductive sheet 2 of a resilient material, a plurality of spacing members 3 attached to the lower surface of the upper conductive sheet 2 and formed of an insulating material, and a top layer 4 of an insulating material. The top layer 4 is overlaid on the upper conductive sheet 2 and is resiliently deformed together with the upper conductive sheet 2 upon striking.
Each of the spacing members 3 attached to the lower surface of the upper conductive sheet 2 has a semispherical configuration and a predetermined diameter. As will be seen from FIG. 2, the spacing members 3 are arranged in rows and columns and each spacing member 3 in any one of the rows is spaced from the adjacent spacing member or members in the same row by a preselected distance. Each of the spacing members 3 in any one of the columns is also spaced from the adjacent spacing member or members in the same column by the preselected distance so that every two adjacent spacing members 3 in each row and two adjacent spacing members confronted therewith and belonging to the next row define a rectangular space having a constant area. A certain difference voltage is applied between the lower conductive sheet 1 and the upper conductive sheet 2, and the upper conductive sheet 2 is subjected to deformation and brought into contact with the lower conductive sheet 1 to produce a electrical signal when a performer strikes the top layer 4 with a mallet. The electric signal has a voltage level proportional to a force acting on the top layer 4 upon striking because the larger force a performer applies, the larger contact area the upper and lower conductive sheets 1 and 2 have. This proportional voltage level is preferable to a skilled performer, however beginners can not precisely control the mallets. This means that the beginners need hard trainings so as to perform the electronic percussion system.